False Scandinavia is too far away unless you are launching your attack from Scotland. France is much closer. The northern shores of France and the southern part of England are separated by the English channel which is only 20 miles apart. It is almost like having no separation at all. The hundred year war was fought by France and England for the most part. Other countries entered into it but they did not have a major part.
Disease was a big reason. Whenever Europeans ventured inwards, they were often struck down by malaria, yellow fever, etc. So they often kept to the coast.